FIELD OF THE INVENTION
This invention relates to an apparatus for immersion-cooled superconductor.
The apparatus for an immersion-cooled superconductor is the type in which a conductor is cooled by being directly immersed in low temperature liquid, for example, liquid helium. As is known, this type includes a natural convection system and a forced cooling system. The natural convection system is the one in which a conductor is simply immersed in a low temperature liquid, for example, liquid helium received in a cryostat. In contrast, forced cooling system is one in which a low temperature liquid in the cryostat is forcefully circulated, and a conductor is immersed in the circulating liquid. The natural convection system has a lower cooling capacity than the forced cooling system, but has an advantage over the latter system in that the cryostat has a simpler construction. In contrast, the forced cooling system has the merit of carrying out very effective cooling, though the cryostat has to be fitted with a liquid helium-circulating mechanism.
The above-mentioned natural convection system and forced cooling system are properly selected according to the construction of the apparatus used. However, both systems have the drawback of not being directly applicable to some form of apparatus for cooling a superconductor, for example, a Poloidal magnetic device of superconductive type used with a nuclear fusion reactor as described in "Superconducting Poloidal Magnets for a Tokamak Fusion Reactor" by Applicants, published in September 1976.
With the Poloidal magnetic device of a superconductive type used with a nuclear fusion pile, an amount of magnetizing current changes with time, generally leading to generation of heat in a conductor. Therefore, it may be considered that the forced cooling system having an extremely great cooling capacity has to be applied to the cooling of the Poloidal magnetic device of a superconductive type for a nuclear fusion reactor. However, the forced cooling system is supposed to present difficulties for the reasons given below in being directly applied to the cooling of the Poloidal magnetic device of superconductive type.
In the first place, the Poloidal magnetic device of a superconductive type used for a nuclear fusion reactor is bulky due to its complicated construction, complicating the liquid helium path in the cryostat. As a result, vapour bubbles released from liquid helium in the cryostat are detained in the liquid helium path, preventing some regions of the apparatus from being fully cooled.
In the second place, gas-liquid two-phase streams flow through the cryostat, making it impossible to attain the stable circulation of liquid helium, unless bubbles of helium carried into the liquid helium are properly eliminated, consequently preventing the interior of the cryostat from being effectively cooled.